<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      body {
        position: relative;
      }
      #box1 {
        width: 100px;
        height: 100px;
        background-color: red;
        position: absolute;
      }
    </style>
    <script>
      // 使div根据不同的方向键向不同的方向移动
      window.onload = function () {
        var speed = 10;

        // 创建一个变量表示方向
        var dir = 0;
        setInterval(function () {
          switch (dir) {
            case 37:
              box1.style.left = box1.offsetLeft - speed + "px";
              break;
            case 39:
              box1.style.left = box1.offsetLeft + speed + "px";
              break;
            case 38:
              box1.style.top = box1.offsetTop - speed + "px";
              break;
            case 40:
              box1.style.top = box1.offsetTop + speed + "px";
              break;
          }
        }, 30);
        document.onkeydown = function (event) {
          if (event.ctrlKey) {
            speed = 100;
          } else {
            speed = 10;
          }
          // dir等于按键的值
          dir = event.keyCode;
        };
        // 当按键松开时div不移动
        document.onkeyup = function () {
          dir = 0;
        };
      };
    </script>
  </head>
  <body>
    <div id="box1"></div>
  </body>
</html>
